The present invention relates to a process for recovering hydrophilic organic compounds from aqueous streams containing same by liquid-liquid extraction.
Many valuable hydrophilic organic compounds such as carboxylic acids, sulfonic acids, polyhydroxy compounds, amino acids and amides are produced or utilized within manufacturing processes involving aqueous streams. Examples include production of carboxylic acids via fermentation processes and utilization of sulfonic acids as catalysts for esterification reactions. Various methods, such as, for example, steam stripping, liquid-liquid extraction, liquid-solid adsorption, chromatography and membrane-based methods, are known for recovery of these valuable hydrophilic compounds from aqueous liquor containing same such as, for example, fermentation broths and waste water streams.
For example, U.S. Pat. No. 5,426,219 (W. Lenhardt et al.) discloses a process for recovering an organic acid such as lactic acid from an aqueous solution thereof. The process involves extracting the aqueous solution containing an organic acid with a mixture consisting of water, a mineral acid in quantity effective to maintain pH of the mixture between 1.0 and 4.5, and an oxygenated solvent which has limited solubility with water and the aqueous solution to produce a solvent extract and a first raffinate. The oxygenated solvent has from 6-8 carbon atoms and at least one hydroxyl, ester, ketone, ether, carbonyl or amid group. The solvent extract is then back extracted with an aqueous liquid to produce an organic acid-rich aqueous extract and an organic acid-depleted solvent raffinate.
U.S. Pat. No. 3,556,739 (A. Baniel et al.) discloses a process for extracting a technical-grade phosphoric acid with certain organic solvents selected from the group of ethers, ketones and glycol ethers having from 2 to 15 carbon atoms. These solvents (a) practically do not extract phosphoric acid from an aqueous solution thereof having concentration of phosphoric acid below 35 percent by weight, and (b) extract a substantial portion of phosphoric acid from an aqueous solution thereof having a concentration of phosphoric acid greater than 35 percent by weight.
U.S. Pat. No. 4,322,550 (J. Kimble) discloses a process for recovery of mercaptoalkanoic acids from an aqueous solution thereof by a liquid-liquid extraction operation using at least one alkanoic acid ester and an alkylene glycol ether.
U.S. Pat. No. 5,628,906 (R. Shinnar et al.) discloses a liquid-liquid extraction process wherein a solution of a solute in a native solvent, for example water, is mixed with a primary solvent, which is soluble with the native solvent, and subsequently adding a modifier, which is insoluble with either the native or the primary solvent. By adding the modifier, the solubility of the primary solvent with the native solvent is changed, thereby causing a near instantaneous phase separation. The solute is concentrated in the primary-solvent-rich phase. Examples of some primary solvents are acetaldehyde, acetic acid, acetonitrile, butanoic acid, ethanol, formic acid, methanol, propanoic acid, 1-propanol, 2-propanol, 2-propanone, propenoic acid, pyridine and triethylene glycol dimethyl ether. Examples of some modifiers are 3-methylbutyl ester of acetic acid, benzene, cyclohexane, 1,2-dichloro ethane, methyl isobutyl ketone, tetralin and toluene.
U.S. Pat. No. 4,954,260 (Z. Ludmer et al.) discloses a phase-transition type of forward extraction process, but one that uses a change in temperature to induce the phase transition, rather than a change in solvent composition. It describes a multi-stage counter-current process in which phase transition from a single-liquid phase to two liquid phases occurs in each step. The required phase transition is induced through the use of internal heating and cooling coils or other heat transfer means in each stage. The process requires changing temperature in each stage in order to cross a liquid-liquid phase boundary in each stage.
U.S. Pat. No. 6,229,046 B1 (A. Eyal et al.) and U.S. Pat. No. 6,320,077 B1 (A. Eyal et al.) disclose processes for separating lactic acid from a fermentation broth containing free lactic acid and lactic acid salts. Oxygenated solvents that have a multiple number of functional groups (such as alcohol and ether) are mentioned as useful provided they give favorable partitioning of lactic acid. These solvents, however, are not used as extraction solvent themselves but rather in admixture with a tertiary amine (trialkylamine), which is the extraction solvent.
Known liquid-liquid extraction processes used to recover hydrophilic organic compounds from aqueous feeds tend to be expensive, because of having a large number of steps, unfavorable partitioning (uneconomically low K values), poor selectivity for the desired solute, or poor efficiency for recovery of the solvents used. An improved method for recovery of valuable hydrophilic organic compounds from aqueous streams has now been discovered. This method uses certain glycol ethers having specific partition ratio, value K, in known liquid-liquid extraction equipment.